The present invention relates generally to an adjustment of driving in a disc drive, and more particularly to an apparatus that corrects weight imbalance (simply referred to as “imbalance” hereinafter) around an axis of the spindle motor. The present invention is suitable, for example, for an apparatus that corrects the disc rotating balance in a hard disc drive (“HDD”).
Along with the recent spread of the Internet etc., a demand for fast recording of a large amount of information is growing. A magnetic disc drive, such as an HDD, is required to have a larger capacity and an improved response. For the larger capacity, the HDD narrows a track pitch on the disc and increases the number of installed discs. For the improved response, use of a higher speed spindle motor is promoted.
The high-density disc requires highly precise head positioning. It is thus necessary to restrain vibrations applied to and deformations of the discs, and to correct imbalance around the spindle motor axis. A primary factor of the imbalance is an imbalance between the disc and the spindle hub. A method of moving the disc to a balanced position is one known imbalance correcting method.
In the HDD that mounts plural discs 24 around the spindle hub 32 of the spindle motor 30, the imbalance occurs when an interval (positional relationship) between each disc 24 and the hub 32 is not equally set unlike FIG. 10. FIG. 11 is a schematic sectional view showing a relationship between the hub 32 and a pair of discs 24 that have imbalance. In FIG. 11, the upper disc 24 is likely to move in the right arrow direction, the lower disc 24 is likely to move in the left arrow direction, and a moment applies to the hub 32. When the hub 32 receives the moment, the disc 24 vibrates and it becomes difficult to position a head (not shown). A large imbalance amount causes a collision between the head and the disc, a damage of the head, and a loss of data on the disc 24.
FIG. 12 is a schematic sectional view of a conventional balance corrector 10. The balance corrector 10 detects the vibration of a housing or disc enclosure base 22 when a pair of discs 24 are rotated with the spindle hub 32 of the spindle motor 30 in the pre-assembled HDD 20. If the vibration exists, an acceleration sensor 16 outputs a waveform W as shown in FIG. 13. If there is no vibration, the output becomes almost 0. In FIG. 13, the ordinate axis represents the imbalance amount (output of the acceleration sensor 16), and the abscissa axis represents time. It is known that the waveform W is output when the imbalance exists. The balance corrector 10 is mounted with a housing 22 via a rubber member 14 on a plate 12 supported on a base F. The rubber member 14 have an L shape, and the right side surface of the convex is restricted by an inner surface of a right sidewall 12b of the plate 12. The left side surface of the convex contacts a right side surface 22b of the housing 22. An impact applicator 14 fixed onto a left sidewall 12a of the plate 12 contacts an outer side of a left side surface 22a of the housing 22. The acceleration sensor 16 is attached to a right side surface 22b of the housing 22. The impact applicator 14 applies an antiphase impact to the housing 22 so that the output of the acceleration sensor 16 shown in FIG. 13 becomes 0. The impact applicator 14 typically has a cylindrical shape and uses a piezoelectric element.
Other prior art include, for example, Japanese Patent Applications, Publication Nos. 10-134502 and 11-39786.
Disadvantageously, the conventional balance corrector 10 cannot correct the imbalance with high precision. Firstly, the output (amplitude) of the acceleration sensor 16 is weak as shown in FIG. 13. This is because the impact applicator 14 is made of ceramic and has high rigidity, reducing the vibration of the housing 22 which the impact applicator 14 contacts. As a result, the output of the acceleration sensor 16 is subject to noises, and the measurement precision and finally the imbalance correction precision lower. Secondly, since the acceleration sensor 16 is attached directly to the housing 22, the measurement precision lowers. First of all, the acceleration sensor 16 is attached directly to the housing 22, and directly receives the impact from the impact applicator 14. This impact shifts the internal condition of the acceleration sensor 16 from its optimized state, increases the noise component, and lowers the measurement precision. In addition, the imbalance-corrected housing 22 is detached from the balance corrector 10 to complete the HDD 20 by mounting other components on the housing 22. Then, another housing 22 is attached to the balance corrector 10. Therefore, in attaching the housing 22 to and detaching the housing 22 from the balance corrector 10, the acceleration sensor 10 must be arduously attached and detached. The attachment error or attachment/detachment impacts shift the internal condition of the acceleration sensor 16 from the optimized state, increases the noise component, and lowers the measurement precision. Thirdly, the impact applicator 14 that uses a piezoelectric element surface-contacts the housing 22, the alignment between them after the housing 22 is mounted is arduous. In addition, the insufficient alignment cannot correct the waveform W shown in FIG. 13, or needs a long time to correct it.
Each of the balance correctors disclosed in Japanese Patent Applications, Publication Nos. 10-134502 and 11-39786 fixes on a table a base mounted with an impact applicator that uses a piezoelectric element, and applies the impact to the plate that supports the disc drive housing. Therefore, the vibration of the spindle motor is reduced by the impact applicator. The acceleration sensor is attached to the plate, and directly receives the impact of the impact applicator.